During the process of hot rolling in the manufacture of steel sheet or coil, the steel sheet is generally rolled at about 1,100° C. and then taken up in a roll at about 800° C. During the aforementioned process, the steel forms scale on its surface so long as the hot rolling is carried out in the open air. The scale layer can have a thickness of several microns to several tens of microns. The scale layer formed on the steel has a composition and structure varied by differences in the conditions of heat treatment during the process of manufacture, and has thermal and mechanical properties significantly different than the underlying steel. These thermal and mechanical differences can adversely affect the performance and longevity of steel processing equipment (e.g., rollers, presses, and cutters). Therefore, the scale layer is preferentially removed during the processing of the steel sheet, coil, or band.
The removal of this scale from band steel, steel sheet, or coil steel has been carried out by the pickling method which uses a strong acid such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid either independently of each other or as combined suitably. Since the pickling relies on the dissolution by a strong acid, it entails a problem of degrading the working environment. Moreover, disposal of the spent acid and the effluent from the pickling system, a huge investment on equipment is required for.
An alternatively, attempts have been made to physically remove scale from the steel sheet surface by spraying shot balls, grit or a slurry mixture of shot balls or grit with water onto the steel sheet surface. However, these techniques are mostly used together with a pickling process; that is, the surface abrasion of the sheet is often a pretreatment process for increasing the efficiency at which special steels such as stainless steel or electric steel sheets are pickled.